背景
在XULRunner的12.0版本中,它是有效的,但当我尝试将它移植到12.0或更高版本时,它会使应用程序崩溃。主要原因是在sdk v12或更新版本中,开发人员删除了xpcom组件的代理对象,并建议替换它通过使用nsRunnable/nsIRunnable包装对象,并通过函数NS_DispatchToMainThread将调用路由到主线程(单击此处(
我在开发什么
我创建了数据库连接器,它是异步的,通过回调与主线程通信。使用:XULRunner v6,移植到XULRunne v17或以上
//nsIDBCallback.idl
[scriptable, function, uuid(XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX)]
interface nsIDBCallback : nsISupports {
void onInfo(in long phase, in long status, in string info);
}
//nsDBService.h, it is XPCOM component
class nsDBService : public nsIDBService, nsIRunnable
{
public:
NS_DECL_ISUPPORTS
NS_DECL_NSIRUNNABLE
NS_DECL_NSIDBSERVICE
private:
std::vector<nsIThread*> threads;
std::vector<nsIDBCallback*> callbacks;
std::vector<const char*> sqls;
nsIThread* makeNewThread();
void runOperationIfNotBussy();
public:
NS_IMETHODIMP Query(const char *sql, nsIDBCallback *callback);
}
//nsDBService.cpp
// adding query and other data to buffers,
// it's thread safe, there are used mutex's
NS_IMETHODIMP nsDBService::Query(const char *sql, nsIDBCallback *callback)
{
callbacks.push_back(callback);
sqls .push_back(sql);
threads .push_back( makeNewThread() );
//run added operation if db driver is free,
//if driver is bussy then invocation is in buffer and need to wait
runOperationIfNotBussy();
return NS_OK;
}
void nsDBService::runOperationIfNotBussy()
{
//some conditions, test's etc.
//run first operation on list
// RUNNING A THREAD, still ok
if(...) threads.front()->Dispatch(this, nsIEventTarget::DISPATCH_NORMAL);
}
//if this method is used by another thread+db query,
//then other operations can't run and need to wait
//operations are stored and supported like fifo
NS_IMETHODIMP nsDBService::Run(void)
{
//some other operations
//real db operations in background
int32_t phase = 3; //endphase
int32_t code = 0; //ok
const char *msg = "OK";
nsIDBCallback *callback = callbacks.pop();
//wrapping callback function with runnable interface
nsIRunnable *runCallback = new nsResultCallback(callback,
phase,
code,
msg);
//routing event to main thread
NS_DispatchToMainThread(runCallback, NS_DISPATCH_NORMAL);
runOperationIfNotBussy();
}
//nsResultCallback.h
class nsResultCallback: public nsRunnable
{
public:
NS_DECL_ISUPPORTS
public:
NS_DECL_NSIRUNNABLE
private:
nsIDBCallback* callback;
int32_t resPhase;
int32_t resStatus;
const char* resMessage;
public:
nsResultCallback(nsIDBCallback* callback,
int32_t phase,
int32_t status,
const std::string &message)
: callback(callback),
resPhase(phase),
resStatus(status),
resMessage(c_str_clone(message.c_str())) {};
~nsResultCallback();
};
//nsResultCallback.cpp
NS_IMETHODIMP nsResultCallback::Run(void)
{
nsresult rv = NS_ERROR_FAILURE;
try
{
// APP HANDS AND CRUSH !
if(this->callback) this->callback->OnInfo(resPhase, resStatus, resMessage);
}
catch(...)
{
rv = NS_ERROR_UNEXPECTED;
ERRF("nsBackpack::Run call method OnInfo from callback failed");
}
return rv;
}
调用
// *.js
nsDBService.query("SELECT * FROM t", function(phase, code, mes) {
//some UI actions or others db queries
});
问题:
当代码执行如下所示时,应用程序冻结并崩溃:
nsDBService::Query //main thread ok
nsDBService::runOperationIfNotBussy //main thread
nsDBService::threads.front()->Dispatch //run bg thread
nsDBService:Run //bg thread
NS_DispatchToMainThread //main thread
nsResultCallback::Run //main thread
nsIDBCallback::OnInfo //main thread, crash
如果代码执行看起来像这样,那么一切都正常:
nsDBService::Query //main thread ok
NS_DispatchToMainThread //main thread
nsResultCallback::Run //main thread
nsIDBCallback::OnInfo //main thread ok
问题:
当从NS_DispatchToMainThread调用nsIDBCallback,从其他线程调用NS_DisptchToMainThread时,然后从主应用程序线程调用,然后执行失败,我缺少什么,不明白吗?或者后台任务的另一种方法是什么?
无法复制,因为您没有提供一个自包含的完整示例,所以请注意:
我首先注意到的是std::vector
的跨线程访问。你在评论中写了一些关于互斥的东西,所以这可能没问题
存储指向nsIDBCallback
的原始指针无疑是错误的。XPCOM对象被引用计数。因此,一旦Query
方法返回,如果没有其他引用,那么底层对象可能是delete
d,从而在向量中留下一个悬空指针。我认为这就是这里正在发生的事情!您需要保持对象的活动状态,直到线程处理完它,最好是将它放入某个nsCOMPtr<nsIDBCallback>
中,例如nsCOMPArray<nsIDBCallback>
中。
附言:原来这是一个有点老的问题,我错过了。。。很抱歉延迟回答:p